Cross-current turn-off silicon controlled rectifier



July 19, 1966 l. soMos 3,261,985

CROSS-CURRENT TURN-OFF SILICON COIIROLLED RECTIFIER Filed Dec. 2l, 19622 Sheets-Sheet l GATE ,DR/0R ART v CATHO E GA TE /NVENTORJ [srl/ANSOMOS,

July 19, 1966 l. soMos 3,251,935

CROSS-CURRENT TURN-OFF SILICON CONTROLLED RECTIFIER I v Filed Deo. 21,1962 2 Sheets-Sheet 2 WML-LAWN GATE N /O' I" /I3 Ym m mi J -AZ /NVENTOR.

./'sTvA/V Somos,

ATTORNEY.

www /4 P N United States Patent O 3,261,985 CROSS-CURRENT TURN-OFFSILICON CONTRGLLED RECTHFIER Istvan Somos, Drexel Hill, Pa., assignor toGeneral Electric Company, a corporation of New York Filed Dec. 21, 1962,Ser. No. 246,446 9 Claims. (Cl. 307-885) This invention relates tosemiconductor devices and, more particularly, to PNPN semiconductordevices of the type that is capable of being switched readily betweentwo extremes of impedance and an object of the invention is theprovision of a simple, reliable and improved device of this character.

More specifically, the invention relates to PNPN semiconductor devicesof the type known as silicon controlled rectifiers. Such a devicetypically comprises a body of silicon having a pair of main electrodes,known as anode and cathode, and a control electrode or gate, with threealternately poled PN (rectifying) junctions being disposed in seriesbetween the main electrodes. It has the characteristic of being capableof remaining in either a high impedance condition (in which it blockscurrent in either direction) or a low forward impedance condition (inwhich it freely conducts conventional current from anode to cathode)without a continuously applied control signal. Silicon controlledrectifiers are functionally similar to gas tube thyratrons, which arecapable of controlling large amounts of current by means of relativelysmall power pulses. Although a silicon controlled rectifier may readilybe transferred from the high impedance mode of operation to the lowimpedance mode in response to the supply of relatively small firingpulses of current to the gate, switching from the low impedancecondition to the high impedance condition to effect turnoff is much moredifficult. A conventional manner of effecting turnoff of a siliconcontrolled rectifier has been to apply a reverse voltage to its anodeand cathode. This reverse voltage causes a reverse recovery currentthrough the device which removes the carriers from the end junctions ofthe device in a brief interval, c g., 1 to 5 microseconds. The remainingcarriers, particularly those in the vicinity of the middle PN junction,disappear by recombination because the reverse current is terminatedwhen the carrier concentrations at the end junctions reach theequilibrium point. The recombination time is relatively long and makesthe turnoff time correspondingly long. If the reverse bias voltage isterminated before recombination has proceeded substantially tocompletion and forward bias voltage exists across the anode and cathode,the silicon controlled rectifier will break over and start conductingagain. Accordingly, a further object of this invention is the provisionof a silicon controlled rectifier in which the high impedance conditionor blocking state is attained and complete turnofl' effected in asubstantially shorter time, i.e., within a few microseconds ofinitiation of the turnoff operation.

In carrying the invention into elect in one form thereof, theintermediate P zone of a PNPN semiconductor silicon controlled rectifieris provided with an auxiliary electrode of P type conductivity materialand the intermediate N type conductivity zone is provided with anotherauxiliary electrode of N type conductivity material so that theseelectrodes and the intermediate P and N zones of the P and N deviceconstitute a diode having a rectifying junction in common with themiddle rectifying junction of the PNPN device. Connections are providedlfor supplying a reverse voltage to these auxiliary electrodes to causecurrent through such diode rectifier that crosses the main current pathin the device and removes the injected minority carriers from the commonmiddle Patented July 19, 1966 invention, reference should now be had tothe following specification and to the accompanying drawings in which:

FIG. 1 is a block layer diagram of a conventional prior art siliconcontrolled rectifier with characteristic curves of the injected minoritycarrier concentration within each of the separate P and N zonesrepresented by characteristic curves.

FIG. 2 is a diagram of a PNPN semiconductor silicon controlled rectifierdevice embodying the invention.

FIG. 3 is a block layer diagram of a portion of a PNPN siliconcontrolled rectifier embodying the invention with injected carrierconcentration within each of the separate P and N zones represented bycharacteristic curves to facilitate an understanding of the operation ofthe invention.

FIG. 4 comprises a plan view and a view in front elevation of a PNPNsilicon controlled rectifier embodying the invention.

FIG. 5 is a view in elevation, partly in section of a modification andFIG. 6 is a sectional view of another modification.

Referring now to the drawings, and particularly to FIG. 1, aconventional silicon controlled rectifier device 1 is conventionallyillustrated as having four zones arranged in succession with contiguouszones of opposite conductivity type so that in order from right to leftthe Zones are designated PNPN. The junctions between contiguous P `and Nzones in order from right to left are denoted J1, J2 and I3. The end Pzone functions as an anode and the end N zone functions as a cathode.Connected by ohmic contact to the intermediate P zone is a gateconductor denoted GATE. With the anode connected to the positiveterminal of a suitable source and the cathode connected to the negativeterminal, forward conduction through the PNPN silicon controlledrectifier can be initiated by supplying a firing pulse of current to thegate contact to switch the device from the blocking state to theconducting state. During its normal conducting state the forward currentis in the direction of the arrow designated If and the distribution ofinjected minority carrier concentration in the forward direction in thefour zones is represented by the solid line curves 2, 3, 4 and 5. The Pequilibrium value in the internal N zone is represented by thehorizontal line 6 and the N equilibrium value in the internal P zone isrepresented by the horizontal line 7.

Conventional practice in turninor off the silicon controlled rectifierhas been to apply a negative bias voltage or Iin other words to reversethe polarity of the voltage supplied to the anode and cathode. When thisreverse voltage is applied, the holes and electrons in the vicinity ofthe two end junctions J1 and .T3 (RFIG. 1) diff-use to these junctionsand produce a reverse (recovery) current in the external circuit that isrepresented by the arrow designated Ir. The directions of movement ofthe injected minority carriers in the intermediate P and N zones duringthis process of removal from the end juncftions is represented by thearrows in the shaded areas. Within one or two microseconds after theapplication of the reverse voltage this reverse current fr sweeps theinjected minority carriers from the end junctions .T1 and J3. Thecarrier distribution in the intermediate N zone is then represented bythe broken line curve 8 and the carrier distribution in the intermediateP zone is represented by the broken line curve 9. Thus, as indicated bythese carrier distribution curves the concentration of injected carriersat the end junctions I1 and I3 is reduced to the equilibrium value. Thisis accomplished within a few microseconds of the application of reversebias voltage and these junctions then assume a blocking state. Recoveryof the silicon controlled rectifier is not complete, however, becausethere is still a high concentration of injected minority carriers in thevicinity of the middle junction J2. All these carriers represented bythe shaded areas under curves S and 9 must disappear by recombinationbecause the reverse (recovery) current ceases when injected minoritycarriers are swept out of rthe end junctions I1 and J3 and the carrierdistribution at these junctions attains equilibrium value. After thehole `and electron distribution at junction J2 has decreased to a lowvalue as a result of the recombination process, this junction regainsits blocking state and a forward voltage may be applied to the siliconcontrolled rectifier without causing it to turn on. However, thisrecombination process takes a relatively long time, eg., between 10 andmicroseconds and this makes the turnoff time correspondingly long. Incertain applications, such for example as high frequency inverters along turnoff time is disadvantageous.

The present invention greatly reduces the t-urnoff time, e.g., itreduces it to the order of one or two microseconds. In the embodiment ofthis invention that is diagrammatically represen-ted in FIG. 2, the fourzone semiconductor device 16 has an intermediate P zone 11 and anintermediate N zone 12. These zones and the junction between them may beformed from a wafer of silicon by any suitable method such, for example,as precision gaseous diffusion techniques. In a fairly typical devicethe thickness of this wafer may be approximately 10 mils and itsdiameter may be in the neighborhood of 1.5 centimeters. On a portion ofthe :dat outer surface of the P zone 11 is formed a zone 13 of N typeconductivity, and on a portion of the parallel outer surface of theintermediate N zone 12 in register with the opposite end N zone 13,there is disposed an auxiliary zone 14 of N type conductivity. Zones 13and 14 may be formed of any suitable material and in any appropriatemanner, e.g., they m-ay be formed of gold foil plus antimony and may beformed on the surfaces of zones 11 and 12 by alloying the gold foil plusantimony strip into the surfaces of the silicon wafer or by any othersuitable method. These zones 13 and 14 may also be formed by gaseousdiffusion and masking techniques or by the vapor deposition method th-atis known in the art as the epitaxial process.

On another portion of the iiat outer surface of P zone l11 is formed anauxiliary zone 15 of P type conductivity; similarly on the exposed lowersurface of N zone 12 is formed a Zone 16 of P type conductivity inregister with the auxiliary P zone 15. Consequently, as is shown in FIG.2, the end P zone 16 of my invention is laterally offset with respect tothe end N zone 13. The P zones I15 and 16 may be formed in any suitablemanner. For example, they may be formed by alloying aluminum strip intothe exterior surfaces of the silicon wafer, i.e., zones 11 and 12 or byutilizing diffusion and masking or epitaxial processes. A g-ateconductor, designated GATE is connected to the P conductivity type zone11. in some cases with the use of appropriate circuitry the auxiliary Pzone 15 may be used as the gate contact.

The zones 16, 12, 11 and 13 constitute a four zone PNPN semiconductordevice and together with the gate constitute a silicon controlledrectifier of which the end P type conductivity zone 16 constitutes theanode and the end N type conductivity zone 13 constitutes the cathode.This rectifier has three alternately poled rectifying junctions J1, J2and 13 in series between anode and cathode. For conduction in theforward direction, the anode 16 is connected to the positive terminal ofa supply source 17 and t-he cathode 13 is connected through a load 18 tothe negative terminal of the source, whereby forward voltage is suppliedto the terminal zones of the rectifier. Conduction of main or loadcurrent by the PNPN silicon controlled rectifier is initiated bysupplying a firing pulse of current to the GATE. For this purpose, as iswell known in the art, suitable external triggering means (not shown)can be connected between the intermediate P zone 11 and the cathode 13.Due to the laterally offset arrangement of the anode 16 and the cathode13, the main current conduction takes place in a diagonal directionthrough the silicon controlled rectifier from the anode 16 at the lowerright hand corner of the device through N type zone 12, P type zone 11to the cathode 13 in the upper left hand corner of the device Thisforward current traverses an appreciable area in the midsection of themiddle NP junction J2 of the device 10 in the direction generallyindicated by the arrow If.

The auxiliary N type zone 14, N type zone 12, P type zone 11 andauxiliary P type zone 15 constitute a PPNN semiconductor device which inpractical effect is a PN diode having a single rectifying junction J2 incommon with the middle junction J2 of the PNPN device. The auxiliaryzones 14 and 15 have been so arranged that this PPNN diode deviceprovides an auxiliary conducting path along a diagonal that crosses thediagonal main conducting path of the PNPN device. In this diode devicethe auxiliary N type Zone 114 and the auxiliary P type zone 15 serve asturnofr electrodes having terminals which may be connected through anexternal diode rectifier 19 and the conductor 2t) to a suitable sourceof direct voltage that is represented by supply terminals 21. A suitableswitching device 22 is included in these connections.

As shown, the diode rectifier 19 in the external circuit is connected toconduct in the direction of reverse current through the PN diode 15, 11,12, 14. This reverse current is represented by the arrow Ic. It will benoted that both the auxiliary current Ic, which flows in a reverse sensebetween the P and N auxiliary electrodes 15 and 14 of the dioderectiiier, and the main current If, which iiows in a forward sensebetween the anode 16 and the cathode 13 of the PNPN device, pass throughthe common junction J2 from zone 12 to zone 11 in the same electricaldirection but on cross diagonal paths, with the auxiliary currentcrossing the main current over the whole area of J2 that is traversed bythe latter. Typically, the voltage source 17 for the PNPN siliconcontrolled rectitier may be in the neighborhood of 400 volts whereas thevoltage of source 21 for the PPNN diode device may be a Very much lowervalue.

To turn on the PNPN silicon controlled rectifier 10 with forward biasvoltage being supplied from the source 17 through the load to the anode16 and cathode 13, a pulse of firing current is supplied to the GATEfrom external triggering means. This causes the PNPN path to switch fromits high impedance to its low impedance state and to become conductingin the forward direction with the result that forward current issupplied to the load 18. During conduction in the forward direction thedistribution of injected carriers in the individual P-N-P-N zones 15,12, 11 and 13 respectively is represented in the concentration diagramin FIG. 3 by the solid line curves 23, 24, 2S and 26 respectively. Acomparison of FiIG. 3 and FIG. 1 indicates that the concentrationdistribution of injected carriers during normal main current conductionin the forward direction is essentially the same as in the case of theconventional silicon controlled rectifier.

To turn ofi the PNPN silicon controlled rectifier 10, i.e., to enablethe PNPN path through zones 16, 12, 11 and 13 to regain forward blockingability, the switching device 22 is closed to apply a reverse biasvoltage across the PPNN diode 15, 11, 12, 14. This immediately resultsin an auxiliary current Ic in the diagonal diode path having the sameelectrical direction across the middle junction J2 as the main currentIf then iiowing in the PNPN silicon controlled rectifier path. Thecurrent Ic, which is a reverse current in `the diode path, effects a netremoval of the injected minority carriers from the NP junction J2. Thedirections of movement of the carriers in this removal process from themiddle junction are represented by the arrows 27 in the shaded areas ofthe intermediate P and N zones in FIG. 3. As shown, the directions areoposite to the directions represented by the arrows in FIG. 1 producedby the conventional turnoff method. Within a period of approximately onemicrosecond after initiation of turnoff, the carriers are swept out ofthe middle junction J2 and the concentration in the intermediate P and Nzones 11 and 12 is represented by the broken line curves 28 and 29. Asindicated by these curves the concentration at the middle junction isreduced to the equilibrium values on both sides of this junction andthis prepares the junction to regain its blocking ability. However, atthis instant recovery of the PNP-N silicon controlled rectifier is notcomplete owing to the concentration of carriers at the end junctions J1and J3 as represented by broken line curves 28 and 29. Consequently, theauxiliary current Ic, which is the recovery current for the junction J2,continues until these carriers are all removed and then terminates. Upontermination of the auxiliary current the junction J2 regains itsblocking state. Recovery of the PNPN silicon controlled rectifier 16,12, 11 and 13 is now complete, and main current conduction will notresume even though the device remains connected to the forward voltagesource 17. The time required from initiation of the auxiliary current inthe PPNN diode until complete turnoff and recovery of the PNPN siliconcontrolled rectifier is 'complete is of the order of a few microseconds.

The auxiliary current Ic required to reduce the injected carriers in theintermediate P and N zones 11 and 12 to equilibrium is very considerablysmaller than the forward current If of 'the silicon controlledrectifier. Consequently, a high value forward current can be interruptedby a low value current pulse. For example, a forward current of 200amperes can be interrupted by a low value current pulse of 20 amperes.

In the form that is illustrated in FIG. 4 the end N type conductivityzone 13 of the PNPN semiconductor device and the additional P typeconductivity zone of the PPNN diode device have the form of parallel,closely spaced rectilinear strips that are located on opposite sides ofan axis generally perpendicular to the NP junction of the internal zones12 and 11 of the device; the end P type conductivity zone 16 (anode) andthe additional N type conductivity zone 14 will have the same form.

In the modification that is illustrated in FIG. 5 the end N typeconductivity zone 13 (cathode) of the PNPN device has the form of anannulus and the additional end P type conductivity zone 15 of the PPNNdevice has the form of a circular disk within the annulus 13. Similarly,the additional end N type conductivity zone 14 has .the form of anannulus disposed in register with the cathode 13, and the end P typeconductivity zone 16 (anode) has the form of a coaxial disk within theannulus.

In this modification main current traverses a predeter- 'mined annulararea of the middle junction J2 of the PNPN silicon controlled rectifierdevice in the direction represented by the arrows If. The reversecurrent of the -PPNN diode path takes place in the same electrical'direction across the same annular area of the common middle junction J2on a cross diagonal axis as indicated :by the arrow Ic. Instead of beingin the form of disks `the zones 15 and 16 may be in the form of rings asillustrated in the modification of FIG. 6. The operation of themodifications illustrated in FIGS. 5 and 6 is the same as described inconnection With FIG. 2.

The device may also be utilized in present inverter 'circuits in whichturnof in each cycle is effected by applying a reverse bias voltage tothe anode and cathode.

When thus used a constant D.-C. bias voltage will be applied to thediode electrodes 14 and 15. In this case, owing to the reverse biasvoltage applied to the anode and cathode the turnoif is in accordancewith the process herein described and referred to as the conventionalprocess. However, .the turnolf time will be reduced t0 the range of 5-10microseconds or less.

The device may also be used, with appropriate circuitry,

as a square wave generator. For this purpose, an adjustable impedance 23is included in series relationship in the PPNN diode circuit. Byadjusting this impedance the current Ic may Ibe adjusted to a value lessthan the critical value required to effect complete turnof action.

As a result, retiring of the device occurs after interruption of theforward current and this procedure is repeated continuously to providecontinuous oscillation.

Alterations and modificationswill readily suggest themselves to personsskilled in the art without departing from the true spirit of thisinvention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A semiconductor translating device comprising:

(a) a circular semiconductor single crystal silicon Wafer having a mainP type conductivity zone and a contiguous main N type conductivity zonein flat face to at face contact,

(1b) the exterior at face of each of said main zones :being providedwith a radially centrally disposed zone of one type conductivity and asurrounding concentric annular zone of the opposite type conductivity toconstitute (1) a PNPN semiconductor device with the terminal P and Nzones constituting -an anode and -a cathode respectively and (2) a PPNNsemiconductor device having terminal electrodes and a PN junction incommon with the middle junction of said PNPN semiconducltor device,

(c) one of said main zones of said PNPN device being provided with meansfor receiving a pulse of firing current to initiate conduction throughsaid PNPN device, and

(d) means for supplyin-g a voltage to said terminal electrodes of saidPPNN device to cause a reverse current through said PPNN device whensaid PNPN device is conducting to remove injected carriers from saidcommon junction to terminate conduction through said PNPN device.

2. A semiconductor translating device comprising:

(a) a semiconductor body including four zones arranged in successionwith contiguous zones of opposite conductivity type to constitute a PNPNsemiconductor device having three PN junctions disposed in generallyparallel planes and having an axis that is perpendicular to all of saidplanes, with the end P and N zones of said PNPN device beingrespectively located on opposite sides of said axis,

(b) the intermediate P zone of said PNPN device being provided withmeans to receive firing current to turn on said PNPN device,

(c) the intermediate P and N zones of said PNPN device each bein-gprovided with a turnoff electrode on the opposite side of said axis fromthe corresponding end zone of said PNPN device thereby to provide adiode rectifier having a single rectifying junction that is in commonwith the middle PN junction of said PNPN device and having a conductingpath that crosses the conducting path between the end zones of said PNPNdevice and (d) said turnof electrodes being adapted to receive a voltagehaving a polarity to cause a reverse current through said diode whensaid PNPN device is conducting vto remove injected carriers from saidcommon junction thereby to turn off said PNPN device.

3. A semiconductor translating device comprising:

(a) a semiconductor body having a Wafer-like zone of P type conductivityand a contiguous wafer-like zone of N type conductivity in at tace toflat face contact to form an internal PN junction therebetween, saidbody having an axis of symmetry that is generally perpendicular to saidjunction,

(b) each of said zones having an exterior at face disposed parallel 'tosaid internal PN junction and provided With two parallel strip zones ofopposite conductivity types with the P type strip zones arranged on oneside of said axis and the N type strip zones arranged on the oppositeside of said axis thereby to constitute (l) a PNPN semiconductor deviceand `(Il) a PN diode provided with P and N type conf ductivity turnoffelectrodes and having a PN junction in common with said internaljunction of said PNPN device and a conducting path that crosses theconducting path of said PNPN device,

(c) one of the zones of said PNPN device being provided with means forreceiving a pulse of firing current to initiate conduction through saidPNPN device, and

(d) terminals connected to said turnof electrodes and adapted to beconnected to a source for supplying to said turno electrodes a voltagehaving a polarity for causing a reverse current through said diode toremove injected carriers from said common junction to effect turnot ofsaid PNPN device.

4. A semiconductor translating device comprising:

(a) a circular semiconductor body having a waferlike P type conductivityzone and a contiguous Waferlike zone of N type conductivity in flat faceto flat face contact,

(b) the exterior at face of both of said zones being provided with aninner annular zone of one type conductivity and an outer concentric zoneof the op posite type conductivity thereby to constitute (l) a PNPNsemiconductor device and y(2) a PN diode device having turnof electrodesand having a PN junction in common with the middle junction of said PNPNdevice and a conducting path that crosses the conducting path of saidPNPN device (c) said Wafer-like P zone of said PNPN device beingprovided with means for receiving a pulse of firing current to initiateconduction through said PNPN device, and

(d) terminals connected to said turnoff electrodes and adapted to beconnected to a source for supplying to said turnott" electrodes avoltage having a polarity to cause reverse current through said diode toremove injected carriers from said middle junction to efect turno ofsaid PNPN device.

5. A semiconductor rectifier comprising:

(a) a semiconductor body having a wafer-like zone of P type conductivityand a contiguous wafer-like zone of N type conductivity in face-to-facecontact to form -an internal PN junction therebetween, said P zone andsaid contiguous N zone respectively having outer surfaces that aregenerally fiat and parallel to each other;

(b) a iirst portion of the outer surface of said P zone being providedwith an end zone of N type conductivity and a first portion of the outersurface of said contiguous N zone being provided with an end zone of Ptype conductivity to form a PNPN semiconductor device, With the end Pzone and the end -N zone constituting main electrodes of said PNPNdevice;

(c) means connected across at least one of the PN junctions of said PNPNdevice for initiating main current conduction through said PNPN device;

(d) a second portion of said outer surface of the rst mentioned P zonebeing provided with a first auxiliary electrode and a second portion ofsaid outer surface of the contiguous N zone being provided with a second.auxiliary electrode to form a PN diode whose PN junction is in commonwith the internal PN junction of said PNPN device, said PN diodeproviding between said auxiliary electrodes a conducting path forauxiliary current that crosses the main current in said PNPN device; and

(e) means connected to said auxiliary electrodes for initiatingauxiliary current conduction in a reverse direction through said P-Ndiode to remove injected carriers from said common middle junction toeffect turnof of said PNPN device.

6. The rectifier of claim 5 in which said end N zone is laterally offsetwith respect to said end P zone and in register with said secondauxiliary electrode, and in which said first auxiliary electrode islaterally offset with respect to said second auxiliary electrode and inregister with said end P zone.

7. For use in combination with a load current circuit, a firing currentcircuit, and a turnoi current circuit, a semiconductor translatingdevice comprising:

(a) a semiconductor -body including four zones arranged in successionwith contiguous zones being of opposite conductivity types to provide aPNPN semi- `conductor device having a PN junction, an NP junc tion, andanother PN junction in series between the terminal P and N zonesthere-of;

(b) means for serially connecting said terminal P and `N Zones in theload current circuit, whereby load *current can flow in a forwarddirection between said terminal P zone and said terminal N zone when thePNPN device is turned on;

(c) means for interconnecting one of said four zones 'of said body andthe tiring current circuit to supply a firing current to turn on thePNPN device;

(d) a pair of auxiliary electrodes respectively connected to theintermediate P and N zones of said body to Iprovide therewith a dioderectifier having a single rectifying junction that is in common withsaid fNP junction of the PNPN device, said auxiliary electrodes being soarranged that reverse current therebetween crosses said load currentover the whole NP junction area that is traversed by said load current;and

(e) means for serially connecting said auxiliary elec trodes in theturnoff current circuit, the latter means being so arranged that theturnoi current will flow in a reverse direction through said `dioderectifier to remove injected carriers from said common NP junc tion toeffect turnoff of the PNPN device.

8. The semiconductor translating device of claim 7 in which the meansfor interconnecting one of said four zones of said -body and the tiringcurrent circuit comprises a gate contact connected to the intermediate Pzone of saidbody.

9. For use in combination with a rst voltage source having relativelypositive and negative terminals and a second voltage source havingrelatively ypositive and negative terminals, a semiconductor translatingdevice comprising:`

(a) a semiconductor body including four zones arranged in successionwith contiguous zones 'being of opposite conductivity types to provide athree-junction PNPN semiconductor device, the terminal P and N zones ofsaid body, respectively constituting anode and cathode of the device,being laterally offset with respect to each other;

(b) Ymeans for connecting said anode to a positive terminal of the tirstvoltage source and said cathode to a negative terminal of the tirstvoltage source;

(c) first and second turno electrodes respectively connected to theintermediate IP and N zones of said body to provide therewith a dioderectifier having a PN rectifying junction in `common with the middlejunction of the PNPN device, said rst turnofrr electrode 'being formedby P type conductivity material and being disposed in register with saidanode, and said second turnoff electrode being formed by N typeconductivity material and being disposed in register with said cathode;and

(d) means for connecting said rst turnoff electrode to a negativeterminal of the second voltage source and said second turnoff electrode-to a positive terminal of -the second voltage source to vcause areverse current through said diode rectier thereby to remove injectedcarriers from said common middle junction to eiect turno action of IthePNPN device.

References Cited bythe Examiner UNITED STATES PATENTS OTHER REFERENCESUnique Properties of the Four-Layer Diode, by Shookley; ElectronicsIndustries and Tele-Tech, August 1957, page 60.

JOHN W. HUCKERT, Primary Examiner.

I. D. CRAIG, Assistant Examiner.

1. A SEMICONDUCTOR TRANSLATING DEVICE COMPRISING: (A) A CIRCULARSEMICONDUCTOR SINGLE CRYSTAL SILICON WAFER HAVING A MAIN P TYPECONDUCTIVITY ZONE AND A CONTIGUOUS MAIN N TYPE CONDUCTIVITY ZONE IN FLATFACE TO FLAT FACE CONTACT, (B) THE EXTERIOR FLAT FACE OF EACH OF SAIDMAIN ZONES BEING PROVIDED WITH RADIALLY CENTRALLY DISPOSED ZONE OF ONETYPE CONDUCTIVITY AND A SURROUNDING CONCENTRIC ANNULAR ZONE OF THEOPPOSITE TYPE CONDUCTIVITY TO CONSTITUTE (1) A PNPN SEMICONDUCTOR DEVICEWITH THE TERMINAL P AND N ZONES CONSTITUTING AN ANODE AND A CATHODERESPECTIVELY AND (2) A PPNN SEMICONDUCTOR DEVICE HAVING A TERMINALELECTRODES AND A PN JUNCTION IN COMMON WITH THE MIDDLE JUNCTION OF SAIDPNPN SEMICONDUCTOR DEVICE, (C) ONE OF SAID MAIN ZONES OF SAID PNPNDEVICE BEING PROVIDED WITH MEANS FOR RECEIVING A PULSE OF FIRING CURRENTTO INITIATE CONDUCTION THROUGH SAID PNPN DEVICE, AND (D) MEANS FORSUPPLYING A VOLTAGE TO SAID TERMINAL ELECTRODES OF SAID PPNN DEVICE TOCAUSE A REVERSE CURRENT THROUGH SAID PPNN DEVICE WHEN SAID PNPN DEVICEIS CONDUCTING TO REMOVE INJECTED CARRIERS FROM SAID COMMON JUNCTION TOTERMINATE CONDUCTION THROUGH SAID PNPN DEVICE.